Which bacteria is the causative agent of gas gangrene?

Correct Answer: C

Rationale: The correct answer is C: Clostridium perfringens. This bacterium is the causative agent of gas gangrene due to its ability to produce gas and toxins in anaerobic conditions. Clostridium tetani causes tetanus, Clostridium botulinum causes botulism, and Bacillus anthracis causes anthrax, not gas gangrene. Clostridium perfringens stands out as the correct choice based on its specific association with gas gangrene and its pathogenic mechanisms.

Correct Answer: D

Rationale: The correct answer is D: Granulomatosis. The appearance of a 10 mm papule 48 hours after the Mantoux test indicates a delayed-type hypersensitivity reaction, which is characteristic of granulomatosis. This type of reaction involves activation of macrophages and T cells, leading to the formation of granulomas. Granulomas are organized collections of immune cells that wall off the antigen, in this case, the tuberculin antigen. A, B, and C are incorrect: A: Cellular cytotoxicity involves the destruction of target cells by immune cells such as cytotoxic T cells or natural killer cells. This mechanism is not associated with the delayed-type hypersensitivity reaction seen in granulomatosis. B: Anaphylaxis is a rapid and severe allergic reaction involving IgE-mediated release of histamine and other inflammatory mediators. This is not the mechanism underlying the delayed-type hypersensitivity reaction in the Mantoux test. C: Antibody-dependent cytotoxic

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent because it is a Gram-positive cocci in pairs with a capsule, which matches the description provided. S. pneumoniae is a common cause of bacterial pharyngitis and can present with sore throat. Summary of other choices: B: Staphylococcus aureus is a Gram-positive cocci in clusters, not pairs, and is not typically associated with sore throat. C: Neisseria meningitidis is a Gram-negative diplococcus and more commonly causes meningitis or septicemia, not sore throat. D: Klebsiella pneumoniae is a Gram-negative rod bacterium, not a Gram-positive cocci, and is not a common cause of sore throat.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. On Endo agar, lactose-fermenting bacteria produce red colonies due to acid production. Escherichersia coli is a lactose-fermenting, gram-negative bacillus commonly found in the intestines. Salmonella and Shigella are lactose-negative and do not produce red colonies on Endo agar. Proteus is also lactose-negative and doesn't typically grow on Endo agar. Therefore, based on the lactose fermentation and colony color, Escherichia coli is the most likely microorganism present in the fecal sample.

Correct Answer: B

Rationale: The correct answer is B: CDC. The Centers for Disease Control and Prevention (CDC) is responsible for establishing hand-washing guidelines in healthcare settings to prevent infections. CDC is a leading authority in public health and provides evidence-based recommendations. OSHA (A) focuses on workplace safety, NIAD (C) is not a recognized organization, and WHO (D) provides global health guidelines but CDC is the primary authority for hand hygiene in the US healthcare system.

Correct Answer: A

Rationale: The correct answer is A: Pseudomonas aeruginosa. Pseudomonas aeruginosa is known to produce green colonies on Endo agar due to its pyoverdin pigment. It is also a Gram-negative rod. P. aeruginosa commonly causes respiratory infections in immunocompromised patients. Escherichia coli (B) typically produces pink colonies on Endo agar and is more associated with gastrointestinal infections. Salmonella typhi (C) and Shigella dysenteriae (D) are both Enterobacteriaceae that usually do not produce green colonies on Endo agar and are more associated with gastrointestinal infections as well.

Correct Answer: A

Rationale: The correct answer is A: aspergillosis and candidiasis. Detection of galactomannan and free mannan is commonly used in diagnosing these fungal infections. Galactomannan is a component of the cell wall of Aspergillus species, while free mannan is associated with Candida species. This detection method helps in identifying these specific fungal infections accurately. B: Syphilis is caused by a bacterium, Treponema pallidum, and is not diagnosed using galactomannan or free mannan detection. C: Leptospirosis is a bacterial infection caused by the Leptospira species and is not diagnosed using galactomannan or free mannan detection. D: HIV infection is a viral infection caused by the human immunodeficiency virus and is not diagnosed using galactomannan or free mannan detection.

Correct Answer: A

Rationale: The correct answer is A: Francisella tularensis. This bacterium is classified as a class A bioterrorism agent due to its high virulence and potential for mass casualties. It can cause tularemia, a severe and potentially fatal disease. The other choices, Hepatitis B, E. coli, and Bacillus subtilis, are not considered class A bioterrorism agents. Hepatitis B is a virus causing liver inflammation, E. coli is a common bacterium found in the gut, and Bacillus subtilis is a beneficial bacterium used in various industries. Therefore, Francisella tularensis is the correct choice based on its high pathogenicity and bioterrorism potential.

Correct Answer: B

Rationale: I apologize for the confusion, but the correct answer to the question is actually A: microtubules. Microtubules are indeed shaped like hollow cylinders made out of tubulin proteins. They play a crucial role in cell structure, cell division, and intracellular transport. Microfilaments (choice B) are composed of actin proteins and are not shaped like hollow cylinders. Intermediate filaments (choice C) are more rope-like in structure and are made up of various proteins. Flagella (choice D) are whip-like structures used for cell movement and are not shaped like hollow cylinders.